agentydragon(tasks): implement context-left indicator in TUI

codex-rs/tui/tests/context_percent.rs

@@ -0,0 +1,54 @@
+use codex_core::{ContentItem, ResponseItem};
+use codex_tui::context::{approximate_tokens_used, calculate_context_percent_remaining, max_tokens_for_model};
+
+#[test]
+fn test_approximate_tokens_used_texts() {
+    // 4 chars -> 1 token
+    let items = vec![ResponseItem::Message {
+        role: "user".into(),
+        content: vec![ContentItem::InputText { text: "abcd".into() }],
+    }];
+    assert_eq!(approximate_tokens_used(&items), 1);
+
+    // 7 chars -> 2 tokens
+    let items = vec![ResponseItem::Message {
+        role: "assistant".into(),
+        content: vec![ContentItem::OutputText { text: "example".into() }],
+    }];
+    assert_eq!(approximate_tokens_used(&items), 2);
+}
+
+#[test]
+fn test_approximate_tokens_used_function_calls() {
+    // name.len=2 + args.len=7 -> 9 chars -> ceil(9/4)=3
+    let items = vec![ResponseItem::FunctionCall {
+        name: "fn".into(),
+        arguments: "{\"a\":1}".into(),
+        call_id: "id".into(),
+    }];
+    assert_eq!(approximate_tokens_used(&items), 3);
+}
+
+#[test]
+fn test_max_tokens_for_model_heuristics() {
+    assert_eq!(max_tokens_for_model("model-32k"), 32768);
+    assert_eq!(max_tokens_for_model("MY-16K-model"), 16384);
+    assert_eq!(max_tokens_for_model("foo-8k-bar"), 8192);
+    assert_eq!(max_tokens_for_model("unknown-model"), 131072);
+}
+
+#[test]
+fn test_calculate_context_percent_remaining() {
+    // if used=0, remaining=max -> 100%
+    let items: Vec<ResponseItem> = vec![];
+    let pct = calculate_context_percent_remaining(&items, "foo");
+    assert!((pct - 100.0).abs() < 1e-6);
+
+    // used=1 of max=4k -> ~0.0249%
+    let items = vec![ResponseItem::Message {
+        role: "user".into(),
+        content: vec![ContentItem::InputText { text: "a".into() }],
+    }];
+    let pct = calculate_context_percent_remaining(&items, "4k-model");
+    assert!(pct < 100.0 && pct > 99.0);
+}